1. Field of the Invention
The present invention relates to a ceramic composition comprising main components of Pb(Ni1/3Nb2/3)O3 as a composite perovskite type oxide and PbTiO3 and PbZrO3 as simple perovskite type oxides. In particular, the present invention relates to a piezoelectric ceramic composition which makes it possible to realize a large strain amount while suppressing the relative dielectric constant to be low, and a piezoelectric actuator for an ink-jet head based on the use of such a piezoelectric ceramic composition.
2. Description of the Related Art
In recent years, as the electronic equipment becomes small-sized and intelligent, the piezoelectric ceramic composition becomes more and more important to serve as the solid displacement element to be used for the electronic equipment. At present, a solid solution of PbTiO3—PbZrO3 (hereinafter referred to as “PZT”, if necessary), which is a solid solution composed of perovskite type oxides, i.e., PbTiO3 (hereinafter referred to as “PT”, if necessary) and PbzrO3 (hereinafter referred to as “PZ”, if necessary), is principally used as the piezoelectric ceramic composition.
Further, a solid solution of Pb(Ni1/3Nb2/3)O3—PbTiO3—PbZrO3 (hereinafter referred to as “PNN-PT-PZ”, if necessary), which is obtained by forming a solid solution of a composite perovskite type oxide, i.e., Pb(Ni1/3Nb2/3)O3 (hereinafter referred to as “PNN”, if necessary) with the solid solution described above, exhibits a relatively large strain. Therefore, this material attracts the attention as a next generation ceramic actuator material.
According to a reference document (“Handbook of New Actuators for Precise Control”, edited by Actuator Research Section of Japan Technology Transfer Association (JTTAS), Fujitec Corporation, 1994), the PNN-PT-PZ solid solution exhibits a relatively large strain (up to 0.12%), and the solid solution exhibits a maximum piezoelectric constant d33 (stain amount with respect to unit voltage) in the vicinity of a composition of 50 molar % PNN-35 molar % PT-15 molar % PZ. Further, it is known that the strain is changed in relation to the peak of the composition of 50 molar % PNN-35 molar % PT-15 molar % PZ in accordance with contour lines having such a certain pattern that the strain is decreased as the distance of separation from the peak is increased.
An ink-jet head, which is carried on an ink-jet printer, includes a piezoelectric type head which is constructed such that a piezoelectric actuator is arranged on a wall surface of an ink cavity, and an ink contained in the ink cavity is discharged from an orifice by utilizing a strain generated when the electric power is applied to the piezoelectric actuator. The piezoelectric ceramic composition, which is composed of the PNN-PT-PZ solid solution as described above, can be used as the piezoelectric actuator of the ink-jet head.
In such a situation, it is important to increase the strain amount of the piezoelectric ceramic composition to be used for the piezoelectric actuator in order to realize the miniaturization of the piezoelectric actuator. Further, it is important to decrease the relative dielectric constant of the piezoelectric ceramic composition in order to realize the energy saving by driving the piezoelectric actuator with a low electric power.
The PNN-PT-PZ solid solution exhibits the relatively large strain (up to 0.12%) in the vicinity of the composition of 50 molar % PNN-35 molar % PT-15 molar % PZ. However, the relative dielectric constant is 5900 which is large. As a result, the input electric energy, which is used to effect the high speed response of the piezoelectric actuator, is also increased. Such a phenomenon is not necessarily preferred for the head-driving circuit even when the strain amount of the piezoelectric actuator is large with respect to the electric field. For example, a problem arises such that the head-driving circuit is large-sized.